1. Field of the Invention
The present invention relates to novel hydrophilic semipermeable membranes which can be dried without loss or deterioration in the properties thereof, and which are based principally on polyvinylidene fluoride (PVDF).
2. Description of the Prior Art
PVDF-based membranes are highly attractive, particularly in the field of ultrafiltration and/or microfiltration, because such membranes have good mechanical properties, good resistance to chemical materials, especially to the common organic solvents, and they are easily heat-sterilized (125.degree. C.). However, the PVDF membranes are not hydrophilic and this is a notable disadvantage, especially when they are destined for ultrafiltration and/or microfiltration operations wherein aqueous solutions are employed.
After semipermeable PVDF membranes have been dried, they must be treated, for example, for a few minutes with an aqueous solution containing 80% of alcohol, to impart hydrophilicity thereto, but this procedure is not particularly convenient in industrial facilities requiring the use of such membranes.
Another technique for rendering permeable PVDF membranes hydrophilic consists, for example, in treating it with a base and then reacting it with polyethyleneimine, as described in published Japanese Application, Kokai No. 53/110,680. Such technique, however, entails complex chemical processing.